1. Field of the Invention
The present invention generally relates to sensors and more particularly to photoconductive sensors having improved characteristics.
2. Description of the Prior Art
Photoconductive crystals of lead-tin telluride have been grown by a closed-tube vapor-growth method with subsequent annealing to form p-n junctions, as described in an article entitled "High-Performance 8-14-.mu.m Pb.sub.1-x Sn.sub.x Te Photodiodes" by Kennedy et al, Proc. IEEE, January 1975. However, the utilization of such devices as sensors have been somewhat limited because, even at a low temperature such as 77.degree. K, they usually exhibit a peak photoconductive response of only a very few volts per watt, typically about 2 volts per watt or less. This response is insufficient for most sensor purposes. The observed low photoconductive response is the case even for the most carefully prepared and annealed PbSnTe of the highest quality single crystal structure. Economical high sensitivity photoconductive sensors are desired for various applications in modern technology and current efforts are being made to find convenient inexpensive ways of producing high quality photoconductive materials in film form. Thus far, it has been found to be very difficult and expensive to prepare films having high photoconductive sensitivity as well as high structural strength required in various sensor applications. Accordingly, it would be highly desirable to be able to provide high structural quality stable photoconductive sensors exhibiting improved photoconductive responsivity and detectivity.